N‐Heterocyclic Carbene‐Catalyzed Umpolung Formal [3+3] Cycloaddition of Enals with Isatogens: Access to Fused Indolin‐3‐ones with a Tetrasubstituted Carbon Stereocenter

A novel synthetic method to access fused indolin‐3‐ones with a tetrasubstituted carbon stereocenter has been developed via NHC‐catalyzed umpolung formal 3+3] cycloaddtion of enals with isatogens. This methodology could be also applied for the quick construction of the 6‐5‐5 tricyclic pyrrolo1,2‐a]indole skeleton which is frequently found as a core structure of many indole alkaloids.